1. Field of the Invention
The present invention relates to the field of optics, and in particular, to a terahertz temporal and spatial resolution imaging system, an imaging method and an application thereof.
2. Related Art
With development of semiconductor manufacturing processes and materials, electronic chips have a higher operation speed, a smaller area, and a lower cost. As phase transition of semiconductors with external excitation is determined by transport characteristics of carriers thereof, the study on the carrier transport phenomena is the foundation of semiconductor device research and development. The terahertz (referred to as THz) pulse technique, as a unique far-infrared measurement means, has demonstrated its significant application potential in the current scientific research and industrial detection. Especially in the study on the semiconductor carrier characteristics, as the terahertz pulse has a low photon energy, a narrow pulse width and other characteristics, which may not have a great impact on the carriers' concentration and transport and can achieve transient measurement, the terahertz time-resolved spectroscopy has become an indispensable research method in the semiconductor device research and development. FIG. 1 is a schematic optical view of the terahertz time-resolved spectroscopy used in the study on characteristics of carriers on semiconductors in the prior art. As shown in FIG. 1, a 800 nm near-infrared light I is used to pump semiconductor sample 101 and excite the light-induced characteristics thereof, then a terahertz pulse II interacts with the semiconductor sample 101, to carry sample transient information, and finally, a terahertz light II and a detection light III pass through a detection crystal 102; the terahertz pulse is measured via electro-optic sampling, to observe transient changes of the semiconductor. The terahertz measurement technique is coherent measurement, which can obtain amplitude and phase information of the spectrum simultaneously, so as to realize accurate analysis for semiconductor transient optical constants.
Owing to concentration gradient of the generated carriers on the semiconductor, horizontal and vertical diffusion may be formed. On one hand, during diffusion, the carriers may collide with each other for direct composite or interact with impurities contained in the semiconductor to form indirect composite. On the other hand, if there is an external electric field or a built-in electric field, the carriers may drift and may be scattered with the semiconductor ionized impurities and lattice vibrations. These processes will result in that the overall optical characteristics of semiconductors show unevenness. However, despite the traditional terahertz time-resolved spectroscopy has lots of advantages, due to its measurement constraints, it is necessary to focus the terahertz spot on one point on the sample for detection; thus, it only reflects the time-domain change characteristics of the carriers, but cannot exhibit the spatial distribution characteristics of the carriers caused by diffusion and drift phenomena.